Alcohol control of lightly crosslinked foamed polymer production

ABSTRACT

An expandable ethylenic or styrenic polymer composition for production of lightly crosslinked foamed polymers and a process for controlling the degree of crosslinking of the polymer prior to extrusion foaming. The control is obtained by use of (a) a reversible gas-yielding crosslinking reaction which is delayed in the foam extrusion line in the presence of gaseous products (alcohols) and (b) added amounts of an alcohol such as an aliphatic alcohol. Suitable crosslinking agents include silanes, azido functional silanes, titanates, and amino compounds.

BACKGROUND OF THE INVENTION

This invention relates to an expandable polymer composition and aprocess for preparing lightly crosslinked, extruded, closed-cell foamedpolymer articles from that composition. It particularly pertains toexpandable ethylenic or styrenic polymer compositions containing areversible crosslinking system which permits alcohol control of thedegree of crosslinking of the polymer prior to extrusion foaming.

It is well known to make closed-cell polymer resin foams by the processof extrusion foaming wherein a normally solid thermoplastic polymerresin is heat-plastified and mixed under pressure with a volatilematerial to form a flowable gel which is then passed through a shapingorifice or die opening into a zone of lower pressure. Upon the releaseof pressure, the volatile constituent of the gel vaporizes, forming agas phase cellular structure in the gel which cools to a correspondingcellular foamed solid resin. Desirably, the resulting gas cells aresubstantially uniform in size, uniformly distributed through the foambody, and closed, i.e., separated from each other by membrane walls ofresin.

It is also known that the use of relatively lightly to moderatelycrosslinked polymers generally improves the quality of foamed polymersarticles.

In addition, lightly crosslinking in some instances make possiblefoaming of polymer foams which otherwise cannot easily be produced. Somepolymers such as linear polyethylenes are difficult to foam byextrusion. It is generally believed that poor melt strength togetherwith a sharp change in melt viscosity near the transition temperaturemakes extrusion foaming of linear polyolefins difficult. Since lightcrosslinking increases polymer viscosity and thus broadens the range offoaming temperature, crosslinking would also be desirable from thisstandpoint.

However, a crosslinked polymer is difficult to extrude. As such, pastpractices have ordinarily not involved crosslinking during normalthermoplastic fabrication processing procedures such as production ofextruded foamed polymer articles. As a result, most research works havebeen directed to production of a crosslinked polymer compositionexpandable during post-extrusion secondary foaming. Recently, however,advances have been made in overcoming some of the problems involved.

For example, Corbett U.S. Pat. No. 4,454,086 (assigned to the assigneeof the present invention) discloses making crosslinked styrene polymerfoams by an extrusion process. In Corbett a styrene/acrylic acidcopolymer is lightly crosslinked in the foam extrusion line with amulti-functional epoxy resin. Since covalent bonds formed by theacid/epoxy reactions are not reversible, the scheme calls for a closecontrol of epoxy level or the reaction rate.

In addition, silane and peroxide crosslinkers have been used tocrosslink polyolefin and polystyrene foams which may be produced byusing an extrusion foaming machine. U.S. Pat. Nos. 4,446,254; 4,421,867;4,351,910, and 4,252,906, amongst others, fall into this category.Sugitani U.S. Pat. No. 4,351,910, for example, proposes improving theheat resistance of a polystyrene foam by introducing an organosilanecompound into a styrene series resin. The silane structure is chemicallybonded to the molecular structure of tne styrene series resin byaddition polymerization, by graft polymerization or by free radicals.The degree of crosslinking is disclosed as being temperature dependent.As such, Sugitani states that crosslinking can be delayed by lowtemperature processing since it only proceeds gradually at temperaturesbelow 100° C.

It is also known that crosslinking can be delayed by swelling thepolymer so as to permit working in crosslinking agents at temperaturesbelow the starting point of the used crosslinking agents. Thus, Beckmannet al. U.S. Pat. No. 3,452,123 discloses adding an organic solvent toswell an ethylene polymer and then admixing therein, at a temperaturebelow the starting point of the used crosslinking agent, the propellantand the crosslinking agent. Extrusion of the resulting mass is carriedout at temperatures above the softening point of the swelled compound.This system is said to result in delay of the crosslinking so that it,preferably, occurs in the extrusion die.

Still, the delayed crosslinking system of Slogburg, like thecrosslinking and foaming systems of the others mentioned, is notreversible and therefore requires rather careful temperature andprocessing controls. The need exists therefore for improved means forcontrolling the degree of crosslinking of an expandable polymer prior toextrusion foaming.

SUMMARY OF THE INVENTION

The present invention meets that need by use of a reversiblegas-yielding crosslinking reaction which is delayed in the foamextrusion line in the presence of gaseous products (alcohols) butproceeds further during foam expansion at the die. Thus, thecrosslinking control of the present invention is primarily accomplishedby inclusion of an aliphatic alcohol, along with the blowing agent, inthe polymer admixture.

Since a delayed crosslinking system makes control of crosslinkingeasier, this permits, for example, a high level of crosslinking with theextrusion foaming process. Increased heat distortion temperatures arethe benefits of such a highly crosslinked polymer.

Another advantage of the presence of alcohol in the blowing agent isthat it can accelerate steam expansion by lowering the glass transitiontemperature of the polymer and also by promoting water vaportransmission. Faster permeation of water could result from its enhancedsolubility in the polymer/alcohol phase and its higher diffusivity inthe alcohol-plasticized polymer. On-line steam expansion, in turn, dropsfoam density enabling production of highly expanded polymer foams.

Basically, the foam extrusion process relies on physical equilibriumbetween a polymer and blowing agent. A physical blowing agent is mixedin and equilibriated with the polymer in the foam extrusion line. Theblowing agent remains dissolved and contained in the polymer phase. Uponexposure to atmospheric pressure at the exit of the die, the gelundergoes phase separation. The blowing agent separates from the polymerphase and rapidly diffuses into the microcavities expanding the polymerto a cellular structure.

A gas-yielding reversible reaction can reach a chemical equilibrium inthe foam extrusion line much the same way as the physical equilibriumbetween polymer and blowing agent. The crosslinking reaction of thepresent invention is, thus, one which reversibly produces a gaseousalcohol reaction product. In the foam extrusion line, the gaseousproduct remains dissolved in the polymer, limiting formation ofcross-bonds to an equilibrium level. At the die during foam expansion,the volatile product rapidly diffuses into the cell cavities depletingits concentration in the polymer phase and letting the reaction proceedfurther. The in situ formed additional cross-bonds help set theexpanding bubbles.

For successful implementation of this mechanism:

(1) the crosslinking reaction must be reversible yielding a gaseousproduct and

(2) the gaseous product must possess the properties required for a goodsecondary blowing agent; (a) adequate solubility in the polymer in theline, (b) high diffusivity during foam expansion, (c) low solubility atambient temperature, and (d) low toxicity and flammability.

It has been found that various crosslinking reaction systems whichreversibly yield an alcohol may be used since many alcohols possess therequired secondary blowing agent characteristics. Crosslinking agentswhich do so with ethylenic and styrenic polymers include silanes, azidosilanes, titanates and amino compounds.

Generally, any grafted silane having more than one hydrolyzable group isuseful as the crosslinking agent. The silane may be an organofunctionalsilane of the general formula R R' Si Y₂ in which R represents a vinyl,epoxy or amine functional radical attached to silicon through a siliconcarbon bond and composed of carbon, hydrogen and optionally oxygen ornitrogen, each Y represents a hydrolyzable organic radical and R'represents a hydrocarbon radical or Y. Examples of such organofunctionalsilanes are found in U.S. Pat. No. 3,646,155, which is specificallyincorporated herein by reference. Alternatively, the silane may be analkoxy silane of the general formula R_(a) Si(OR')_(b), where "a" is 1,2and "b" is 2,3, R is methyl or organoreactive alkyl group and OR' is ahydrolyzable alkoxy group, or it may be a hydroxy functional siliconeintermediate. Examples of such alkoxy silanes are found in U.S. Pat. No.4,351,910, which is specifically incorporated herein by reference.

The silane crosslinking agent is preferably one which is bothorganofunctional and alkoxy. Examples of organofunctional alkoxy silaneswhich may be used are gamma-glycidoxypropyltrimethoxy silane,gamma-methacryloxypropyltrimethoxy silane, vinyltrimethoxy silane,vinyltriethoxy silane, N-(2-aminoethyl)-3-aminopropyltrimethoxy silane,N-β-(N-vinyl benzyl amino) ethylaminopropyltrimethoxy silane,methyltrimethoxy silane, and gamma -aminopropyl triethoxy silane.

While all of the crosslinking agents utilized in the present inventionare useful for producing lightly crosslinked polymer foams, the mostpreferred crosslinking agents are the azido functional silanes of thegeneral formula R R'SiY₂, in which R represents an azido functionalradical attached to silicon through a silicon to carbon bond andcomposed of carbon, hydrogen, optionally sulfur, nitrogen, and oxygen,each Y represents a hydrolyzable organic radical, and R' represents amonovalent hydrocarbon radical or a hydrolyzable organic radical.Examples of the azido functional silanes which may be used are found inU.S. Pat. Nos. 3,705,911 and 4,401,598, which are specificallyincorporated herein by reference. Preferred amongst the azido functionalsilanes are 2-(trimethoxysilyl) ethyl phenyl sulfonyl azide and(triethoxy silyl) hexyl sulfonyl azide.

The titanate crosslinking agent may be a titanium alkoxide of thegeneral formula Ti(OR)₄ where R is C₁, to C₁₈ alkyl or it may be atitanate coupling agent of the general formula (RO)_(m) --Ti(O--X--R²--Y)_(n) wherein R is typically alkyl, X is carboxyl, R² is a longcarbon chain, Y is reactive double bond or amino, and m and n areintegers which total 4. Preferred amongst the titanates are titaniumisopropoxide, and tetramethyl titanate.

Preferred as amino crosslinking agents are hexamethoxymethylmelamine(HMMM) and alkylated glycolurilformaldehyde resins.

The ethylenic or styrenic polymer material may be an olefinic polymer orcopolymer; an alpha-olefin polymer with an α,β ethylenically unsaturatedcarboxylic acid, hydroxyl ethyl acrylate or carbon monoxide; a styrenehomopolymer or copolymer; styrene having hydroxyl, carboxylic acid andcarbonyl functional groups; vinyl toluene polymers; or mixtures andblends thereof. For example, the ethylenic or styrenic material may belinear low density polyethylene, high density polyethylene,polypropylene, styrene/acrylic acid copolymers, ethylene/acrylic acidcopolymers, styrene/acrylonitrile/hydroxy ethyl-acrylate terpolymers,and mixtures thereof.

The blowing agent may be selected from conventional physical blowingagents such a chlorofluorocarbons, chlorocarbons, hydrocarbons andalcohols. Preferred are dichlorodifluoromethane,trichloromonofluoromethane, dichlorotetrafluoroethane, and mixturesthereof.

When halogenated hydrocarbon compounds are used as the blowing agent,there can be from about 0.013 to about 0.50 gram mole, and preferably0.040 to 0.30 gram mole of such blowing agent per 100 grams of polymerresin in the admixture.

The alcohol used to control the degree of crosslinking is preferably analiphatic alcohol such as methanol (methyl alcohol), ethanol (ethylalcohol), n-propanol (propyl alcohol), i-propanol (isopropyl alcohol)and butanols (butyl alcohols).

Preferably, the alcohol is added during processing along with theblowing agent. For example, an 80/20 mixture ofdichlorodifluoromethane/methanol may be used as the blowingagent/alcohol. The weight ratio of blowing agent to alcohol may,however, vary from approximately 70/30 to 95/5.

In some instances, however, an alcohol can serve the dual purpose ofcrosslinking delaying and blowing agent when used with a crosslinkingagent in accordance with the present invention. Alcohols are somewhatdeficient in blowing power with their low vapor pressure and highsolubilities in certain polymers. Lightly crosslinking permits raisingthe foaming temperature and thus the blowing efficiency leading to lowfoam densities. Thus, it is possible to use alcohol alone as the blowingagent/crosslinking control with certain crosslinking agents andpolymers.

In any event, addition of an alcohol along with the blowing agentpermits control of the degree of crosslinking when the crosslinkingreaction mechanism is a reversible one yielding alcohols.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For example, the fundamental chemistry involved in silane crosslinkingis depicted by the following reactions: ##STR1## Methoxy silanehydrolyzes reversibly to silanol releasing methanol by reaction (a).Silanols condense to siloxane linkages releasing water by reaction (b).Overall two moles of methoxy silane and one mole of water reversiblyproduce one mole of siloxane crosslink releasing one mole of methanol byreaction (c).

Alkoxy functional silanes graft on ethylenic or styrenic polymers havingcarboxylic acid groups through reaction of carboxylic acids with methoxygroups forming acyloxy silane linkages, again with the release ofalcohol.

Amino functional silanes graft on polymers having carboxylic acid oranhydride groups. Silanes having epoxy functional groups also react withcarboxylic acid-functional polymers such as copolymers of acrylic acidwith ethylene or styrene. Since reversible, alcohol yielding, reactionmechanisms occur with silanes of this type, these crosslinkingmechanisms are controllable by use of an alcohol in the processing.

A titanium alkoxide reversibly reacts with a carboxylic acid or hydroxylfunctional polymer releasing alcohols. Amino crosslinking agents canalso be used to crosslink polymers containing hydroxyl, carboxy or amidefunctionality. Amino crosslinking agents crosslink such functionalizedpolymers through a condensation reaction releasing alcohol as a product.In addition, titanate and amino crosslinking agents are inexpensivepermitting a high level of use without cost penalties.

However, as noted, the silane, titanate and amino crosslinkingmechanisms require a polymer having a functional group such ascarboxylic acids. An azido functional silane is unique in that it cangraft on most polymers through the nitrine insertion reaction: ##STR2##Therefore, an azido functional silane can graft on and crosslinkpolyethylene and polystyrene having no reactive functional group.

Accordingly, azido functional silanes are tne preferred crosslinkingagent and will be used as the illustrative crosslinking agent in thegeneral description of the preferred embodiment which follows. Still, aslong as the reaction between the polymer and the crosslinking agent is areversible one yielding alcohols, it is controllable in accordance withthe instant invention, and various of the following examples illustrateuse of others of the crosslinking agents.

In accordance with the process of the present invention, lightlycrosslinked polymer foams may be made on conventional melt processingapparatus such as by continuous extrusion from a screw-type extruder.Such an extruder typically comprises a series of sequential zonesincluding a feed zone, compression and melt zone, metering zone, andmixing zone. The barrel of the extruder may be provided withconventional electric heaters for zoned temperature control.

An inlet, such as an injection nozzle, is provided for adding a mixtureof fluid blowing agent and crosslinking agent under pressure to thepolymer in the extruder barrel between the metering and mixing zones.Crosslinking agent is pumped, in a controllable manner, into the streamof fluid blowing agent upstream of the injection nozzle. The blowingagent and crosslinking agent are compounded into the starting polymer ina conventional manner to form a flowable gel or admixture, preferably ina continuous manner. Thus, the polymer, blowing agent, and crosslinkingagent may be combined in the mixing zone of an extruder using heat toplastify the polymer resin, pressure to maintain the blowing agent in aliquid state, and mechanical working to obtain thorough mixing.

The blowing agent is compounded into the flowable gel in proportions tomake the desired degree of expansion in the resulting foamed cellularproduct to make products having foamed densities down to about 0.6 pcf.Depending on the amount of blowing agent added, the resulting foamedmaterials may have densities from about 0.6 to 15.0 pcf.

The alcohol for crosslinking control purposes is preferably added withthe blowing agent. As mentioned, the blowing agent/alcohol ratio, byweight, may vary from approximately 70/30 to 95/5.

Since the condensation reaction of silanols to siloxanes is catalyzed bythe presence of certain metal catalysts such as dibutyl tin dilaurate orbutyl tin maleate, it is preferred that when azido silanes are used asthe crosslinking agent in the present invention, that a small amount ofsuch catalyst also be added to the polymer melt.

The crosslinking reaction is self-controlled in the extruder by thepresence of the gaseous reaction product, namely an alcohol, whichlimits the reaction. However, the crosslinking reaction proceeds duringfoam expansion at the exit of the die as the alcohol diffuses into thegaseous phase with the volatile blowing agent.

In this manner, crosslinking of the polymer gel in the extruder iscontrolled so that the gel remains flowable until it exits the die to azone of lower pressure. There, the crosslinking reaction proceeds, whichstabilizes gas bubble and cell formation as the olefinic polymer isexpanded. Because the degree of crosslinking in the extruder can becontrolled, a greater proportion of azido silane crosslinking agent maybe added and, a higher degree of crosslinking in resultant polymer foammay be obtained.

Suitable azido-functional silane compounds include the group of azidotrialkoxysilanes such as 2-(trimethoxysilyl) ethyl phenyl sulfonyl azide(commercially available from Petrarch Systems, Inc., Bristol, Pa.) and(triethoxy silyl) hexyl sulfonyl azide (commercially available as AzcupD-98 from Hercules, Inc., Wilmington, Del.). The azido functional silanecrosslinking agent is added in an amount between about 0.01 to 2.0 partsper hundred (pph), by weight, of ethylenic or styrenic polymer. Anespecially preferred range of addition is between 0.02 to 1.0 pph ofazido silane crosslinking agent.

The discharge end of the mixing zone of the extruder is connected,through a cooling and temperature control zone, to a die orifice. Thehot polymer gel is cooled and then passed through the die orifice into azone of lower pressure (e.g., normal ambient air atmosphere) where theblowing agent is activated and the polymer gel expands to a lowerdensity, cellular mass. As the foamed extrusion forms, it is conductedaway from the die and allowed to cool and harden.

In practice, the temperature of the feed zone is maintained at 180°±20°C., the temperature of the melting, metering, and mixing zones ismaintained at 210°±20° C., and the temperature in the cooling andtemperature control zone is maintained at 120°±20° C. The temperature ofthe polymer gel as it expands through the die orifice is preferably justabove the temperature at which solid polymer would crystallize out ofthe gel and will vary depending upon the particular ethylenic orstyrenic polymer utilized.

The resulting lightly crosslinked polymer foams comprise substantiallyclosed-cell structures and are flexible to bending and shaping. Thefoams have excellent dimensional stability and high compressivestrengths and heat distortion temperatures than branched low densitypolyethylene foams having an equivalent foam density.

As is conventional, finely divided solid materials such as talc,calcium-silicate, zinc stearate, and the like can advantageously beincorporated with the polymer gel prior to expansion. Such finelydivided materials aid in controlling the size of the cells and may beemployed in amounts up to five percent by weight of the polymer.Numerous fillers, pigments, lubricants, and the like well known in theart can also be incorporated as desired. Antioxidants may be added toretard or suppress the crosslinking reaction. In such an instance whereantioxidant is present in or added to the polymer gel, an additionalamount of crosslinking agent may be required to achieve the desireddegree of crosslinking.

The specific working examples that follow are intended to illustrate theinvention but are not to be taken as limiting the scope thereof. In theexamples, parts and percentages are by weight unless otherwise specifiedor required by the context.

EXAMPLE I

The apparatus used in this example is a 11/4" screw type extruder havingtwo additional zones for mixing and cooling at the end of usualsequential zones for feeding, melting and metering. An opening forblowing agent injection is provided on the extruder barrel between themetering and mixing zones. A small syringe-type pump is connected to theblowing agent stream for additive injections. At the end of coolingzone, there is attached a die orifice having an opening of rectangularshape. The height of the opening, called die gap hereinafter, isadjustable while its width is fixed at 0.25".

In this example, it is shown that a high temperature-resistantpolyolefin foam can be produced from a blend of a linear low densitypolyethylene and an ethylene/acrylic acid copolymer. Thus, the polymerused in this example is a 50/50 by weight blend of a linear low densitypolyethylene, Dowlex 2032 (2.0 M.I., 0.926 g/cc density), and Dow PE452, a granular copolymer of acrylic acid with ethylene (2.0 M.I., 0.932g/cc density and 6.5% acrylic acid). Throughout the tests in thisexample, a small amount of talcum powder (0.2-0.7 pph) was added forcell size control. Optionally, a small amount (0.05 pph) of magnesiumoxide was put in to catalyze epoxy/acid reaction.

An 80/20 by weight mixture of FC-12/FC-11(dichlorodifluoromethane/trichloromonofluoromethane) was employed as theblowing agent in the tests of this example. Methanol was fed in theextruder in a mixture with the blowing agent in tests designed to seeits effect as the reaction-delaying agent. Formulations in the test ofthis example are presented in Table A.

The temperatures maintained at extruder zones were approximately 120° C.at feeding zone, 190° C. at melting and metering zone and also at mixingzone. The temperature of cooling zone was maintained so that thetemperature of the polymer/blowing agent mixture could reach an optimumuniform temperature for foaming which was in the range of 115°-119° C.as shown in Table A. The die gap was fixed at 0.120" throughout thetests. In some tests, foam dimensional stability at ambient temperaturewas followed with specimens cut to about 7 inches in length. The foamcross sectional area varied with the formulation but most had width inthe range of 1.0-1.5" and thickness 0.7-1.0".

Table A shows the results of the tests. With no crosslinking, foamresulted in total collapse. Addition of epoxy functional silane made thefoam rise. Magnesium oxide is shown to assist crosslinking. At a Z-6040level of 0.3 pph with magnesium oxide incorporated, a reasonably goodlooking foam of substantially open cell structure was obtained.Dimensional stability of the open cell foam was naturally good. Furtherincrease in crosslinking agent, however, made the foam strand unstable.That is, the foam strand became wobbly and in extreme cases fractured.Note that addition of crosslinking agent raises the extruder dischargepressure as much as 600 psi.

Addition of methanol dramatically reduced the line pressure as seen inTests 9 and 10. Also, addition of methanol cured the flow instability ofthe extruder and further resulted in good foams having substantiallyclosed-cell structure.

The heat distortion characteristics of the blend foam produced in Test10 were tested against a foam produced from a low density polyethylenehaving 2.3 M.I. and 0.921 g/cc density. The blend foam of Test 10 hadsuperior high temperature performance.

                                      TABLE A                                     __________________________________________________________________________                                        FOAM        DIMEN-                            BA   MgO  Z-6040                                                                             MeOH GEL   EXTRUD.                                                                             DEN-                                                                              CELL                                                                              OPEN                                                                              SIONAL FLOW                   TEST                                                                              LEVEL                                                                              LEVEL                                                                              LEVEL                                                                              LEVEL                                                                              TEMP. PRES. SITY                                                                              SIZE                                                                              CELL                                                                              STABILITY                                                                            STABILITY              NO. (1)  (2)  (3)  (4)  (5)   (6)   (7) (8) (9) (10)   (11)                   __________________________________________________________________________    1   22.1 0    0    0    118.5  960  --  --  --  --     Foam Collapses         2   21.0 0    0.2  0    117   1140  2.84                                                                              1.47                                                                              93  --     Foam Rises             3   21.6 0.05 0.2  0    117.5 1340  1.89                                                                              2.03                                                                              92  --     Foam Improves          4   21.0 0    0.3  0    117.2 1340  2.49                                                                              1.62                                                                              93  --     Foam Improves          5   21.1 0.05 0.3  0    117.5 1550  1.71                                                                              1.47                                                                              95  101    Looks Good             6   20.8 0    0.4  0    116   1510  1.69                                                                              1.62                                                                              91  97     Unstable               7   21.6 0.05 0.4  0    116.5 1520  1.69                                                                              1.62                                                                              84  --     Unstable               8   22.7 0    0.5  0    116   1540  1.51                                                                              1.80                                                                              84  99     Unstable               9   17.8 0    0.5  1.98 115    890  1.62                                                                              1.35                                                                              59  --     Verge of                                                                      Prefoaming             10  18.5 0.05 0.5  2.06 116.5 1000  1.53                                                                              1.62                                                                              43  55     Looks                  __________________________________________________________________________                                                           Good                    (1) parts of 80/20 by weight mixture of FC12/FC-11 mixed in per hundred       parts of polymer                                                              (2) parts of magnesium oxide mixed in per hundred parts of polymer            (3) parts of Dow Corning epoxy functional silane Z6040 mixed in per           hundred parts of polymer                                                      (4) parts of methanol mixed in per hundred parts of polymer                   (5) temperature of gel coming out of the die in degrees centigrade            (6) pressure at the extruder discharge in pounds per square inch              (7) density of foam body in pounds per cubic foot measured in about one       month                                                                         (8) cell size in millimeter in horizontal direction determined per ASTM       D3576                                                                         (9) open cell in percent determined per ASTM D2856-A                          (10) minimum or maximum volume of foam body during aging as percentage of     initial volume measured within about five minutes after extrusion             (11) appearance of foam body being extruded out of the die orifice       

EXAMPLE II

The apparatus and its operating procedure used for tests in this examplewere the same as in Example I.

A granular styrene/acrylic copolymer (1% acrylic acid, 200,000 M.W.) wasuniformly mixed with about 0.2 pph talcum powder and 0.2 pph bariumstearate. The mixture was fed into the extruder at an essentiallyuniform rate of about 10 pounds per hour. The blowing agent used was a70/30 by weight mixture of dichlorodifluoromethane (FC-12) and ethanol,which was injected into the extruder at a uniform predetermined rate.The crosslinking agent used in this example is hexamethoxymethylmelamine(HMMM) (CYMEL 303 made by American Cyanamid Co.). A predetermined amountof corsslinking agent was injected in the blowing agent stream in TestNos. 2 through 5 as shown in Table B. The extruder zones were maintainedat 160°, 200° and 200° C. for feeding, melting, metering and mixingzone, respectively. The temperature of cooling zone was maintained toachieve a uniform gel temperature of 145° C. throughout the tests. Whenall temperatures reached a steady state, the effect of die gap on foamappearance and line pressures was determined.

After about a week, the foams were tested for high temperatureresistance. Foam slugs of a about 0.25" thickness are sliced out of foamstrands and subjected to hot air of predetermined temperature for onehour. Percent retention of foam volume after the test was recorded as anindication of collapse resistance.

As shown in Table B, HMMM at a level up to 0.9 pph has a minimal effecton the pressures and, accordingly, the threshold die gap for prefoamingdoes not vary with the HMMM level. At 0.030" die gap, good foams aremade independent of HMMM level. The results clearly substantiate thatalcohol, indeed, delays the crosslinking reaction in the foam extrusionline.

                                      TABLE B                                     __________________________________________________________________________        BA   HMMM DIE                                                                              DIE EXTR.                                                                             FOAM FOAM FOAM                                       TEST                                                                              LEVEL                                                                              LEVEL                                                                              GAP                                                                              PRES.                                                                             PRES.                                                                             THICK.                                                                             WIDTH                                                                              DENS.                                      NO. (1)  (2)  (3)                                                                              (4) (5) (6)  (7)  (8)                                        __________________________________________________________________________    1   1.45 --   0.030                                                                            460 660 0.50 1.12 1.74                                       2   1.44 0.2  0.030                                                                            480 700 0.47 1.22 2.10                                       3   1.46 0.5  0.030                                                                            520 750 0.53 1.21 1.85                                       4   1.47 0.7  0.030                                                                            520 760 0.50 1.27 1.86                                       5   1.47 0.9  0.030                                                                            510 740 0.50 1.34 1.86                                       __________________________________________________________________________        CELL PREFOAMING                                                           TEST                                                                              SIZE (?)      COLLAPSE RESISTANCE (11)                                    NO. (9)  (10)     100 110 115 120 125° C.                              __________________________________________________________________________    1   0.44 verge    136 182 227 32  15                                          2   0.49 verge    140 182 232 39  19                                          3   0.42 verge    143 184 229 46  21                                          4   0.31 verge    145 184 232 47  23                                          5   0.45 no       145 185 226 50  25                                          __________________________________________________________________________     (1) parts of 70/30 by weight mixture of dichlorodifluoromethane and           ethanol mixed in per hundred parts of polymer                                 (2) parts of hexamethoxymethylmelamine (CYMEL 303 made by American            Cynamid) mixed in per hundred parts of polymer                                (3) the gap of die opening in inches                                          (4) pressure at the die in pounds per square inch                             (5) pressure at the extruder discharge in pounds per square inch              (6) thickness of foam body in inches                                          (7) width of foam body in inches                                              (8) density of foam body in pounds per cubic foot determined after 6          months aging                                                                  (10) condition of foam strand coming out of the die: blips = blow holes,      verge = verge of prefoaming, no = no foaming                                  (11) foam volume as a percentage of the initial after aging in an oven of     given temperature for one hour                                           

EXAMPLE III

In the tests in this example, there were used the same apparatus, itsoperating procedure, polymer, blowing agent and cell size control agentas used in Example II. Additionally, there were added one pph FR651A and0.03 pph magnesium oxide. FR651A is a flame retardant manufactured byDow Chemical Company. The extruder zones were set down a little toprevent decomposition of the flame retardant: 140°, 170° and 176° C. forfeeding, melting, metering and mixing zone, respectively. The geltemperature was varied slightly as presented in Table C.

As shown in Table C, HMMM has little impact on die pressure and extruderdischarge pressure manifesting the inhibiting effect of alcohol. Themost remarkable thing with the formulations is improvement in collapseresistance. The threshold temperature for collapse, as defined by themaximum temperature at which foam retains at least 90% of its originalvolume, increases with the HMMM level. It increases from 120° to 125° C.for formulations containing 0.5 to 0.9 pph, 140° C. for one containing1.0 pph and 160° C. for one with 2.0 pph HMMM. It appears that the flameretardant additive catalyzes the crosslinking reaction and that the HMMMneeds to exceed about 1.0 pph to impart significant thermo-collapseresistance to a foam product. However, it is possible to lower therequired level by adding the more potent external catalyst such aparatoluenesulfonic acid.

                                      TABLE C                                     __________________________________________________________________________                  FOAMING                                                             BA   HMMM GEL    DIE                                                                              DIE EXTR.                                                                             FOAM FOAM FOAM                                TEST                                                                              LEVEL                                                                              LEVEL                                                                              TEMP.  GAP                                                                              PRES.                                                                             PRES.                                                                             THICK.                                                                             WIDTH                                                                              DENS.                               NO. (1)  (2)  (12)   (3)                                                                              (4) (5) (6)  (7)  (8)                                 __________________________________________________________________________    1   1.14 --   135    0.040                                                                            450 710 0.58 1.28 2.53                                2   1.49 0.5  144    0.030                                                                            540 750 0.52 1.30 2.05                                3   1.41 0.7  144    0.030                                                                            510 720 0.51 1.23 1.99                                4   1.48 0.9  144    0.030                                                                            480 700 0.44 1.21 1.92                                5   1.31 1.0  135    0.040                                                                            440 680 0.63 1.28 2.02                                6   1.31 2.0  135    0.040                                                                            435 720 0.54 1.28 2.29                                __________________________________________________________________________        CELL                                                                              PREFOAMING                                                            TEST                                                                              SIZE                                                                              (?)      COLLAPSE RESISTANCE (11)                                     NO. (9) (10)     110 120                                                                              125 130                                                                              140 150                                                                              160 170° C.                      __________________________________________________________________________    1   0.90                                                                              no       221 207                                                                               45 34 21  ND ND  ND                                  2   0.46                                                                              verge    177 212                                                                               99 80 36  ND ND  ND                                  3   0.29                                                                              no       179 225                                                                              105 74 29  ND ND  ND                                  4   0.28                                                                              verge    167 201                                                                               95 66 28  ND ND  ND                                  5   0.56                                                                              verge    202 303                                                                              295 189                                                                              103  63                                                                               46 26                                  6   0.35                                                                              verge    202 267                                                                              289 292                                                                              241 158                                                                              118 89                                  __________________________________________________________________________     ND = not determined                                                           (1) parts of 70/30 by weight mixture of dichlorodifluoromethane and           ethanol mixed in per hundred parts of polymer                                 (2) through (11) = the same as in Table B                                     (12) temperature of foaming gel in degrees centigrade                    

Example IV

The apparatus and its operating procedure used in this example was thesame as in Example II. An ethylene/acrylic acid copolymer having 6.5%acrylic acid and 2.0 melt index was evaluated in this work. HMMM (CYMEL303) was used as the crosslinking agent and talcum powder as the cellsize control agent. Three different types of blowing agents, as shown inTable D, were employed to observe the effect of alcohol. The zones ofextruder were set at 150°, 180° and 180° C. for feeding, melting,metering and mixing zone, respectively. The gel temperature wasmaintained at 100°, 104° and 102° C. for FC-12, FC-12/EtOH andFC-114/MeOH blowing agent, respectively.

Table D sets forth the test results. With the absence of alcohol in TestNo. 2, 0.2 pph HMMM is sufficient to overcrosslink the polymer in thefoam extrusion line. Melt fracture of the foam strand accompanied with asharp increase in line pressure plagues the test. Test Nos. 4 and 6demonstrate the reaction-delaying effect of alcohol. At a HMMM level ashigh as 1.5 pph, good foams are made without a large increase inpressures and flow instability. The crosslinked foams show improvementof collapse resistance. The foam made in Test No. 6 contined 42%insoluble gel after an extraction test in boiling xylene for 24 hoursand the polymer was no longer flowable.

                                      TABLE D                                     __________________________________________________________________________        BLOWING AGENT                                                                 TYPE           TALC HMMM DIE                                                                              DIE EXTR.                                                                             FOAM FOAM                             TEST                                                                              LEVEL      (pph)                                                                             LEVEL                                                                              LEVEL                                                                              GAP                                                                              PRES.                                                                             PRES.                                                                             THICK.                                                                             WIDTH                            NO. (12)       (1) (13) (2)  (3)                                                                              (4) (5) (6)  (7)                              __________________________________________________________________________    1   FC-12      20.3                                                                              0.3  --   0.18                                                                             430 1210                                                                              1.44 1.51                             2   FC-12      21.6                                                                              0.3  0.2  0.18                                                                             600 1720                                                                              1.42 1.60                             3   FC-12/EtOH:80/20                                                                         18.8                                                                              0.4  --   0.13                                                                             380  890                                                                              1.23 1.45                             4   FC-12/EtOH:80/20                                                                         18.8                                                                              0.4  0.7  0.13                                                                             435  980                                                                              1.24 1.64                             5   FC-114/MeOH:90/10                                                                        24.3                                                                              0.6  --   0.10                                                                             405 1040                                                                              0.89 1.36                             6   FC-114/MeOH:90/10                                                                        24.4                                                                              0.6  1.5  0.10                                                                             455 1210                                                                              0.79 1.35                             __________________________________________________________________________        BLOWING AGENT                                                                 TYPE       FOAM                                                                              CELL                                                                              PREFOAMING                                             TEST                                                                              LEVEL      DENS.                                                                             SIZE                                                                              (?)      COLLAPSE RESISTANCE (11)                      NO. (12)       (8) (9) (10)     95  100                                                                              105 110                                                                              115° C.                  __________________________________________________________________________    1   FC-12      1.61                                                                              1.01                                                                              verge    96  87 31  30 ND                              2   FC-12      2.18                                                                              1.62                                                                              melt fract                                                                             88  80 26  13 ND                              3   FC-12/EtOH:80/20                                                                         1.97                                                                              1.25                                                                              no       100 97 56  40 29                              4   FC-12/EtOH:80/20                                                                         1.89                                                                              1.25                                                                              no       99  98 85  71 62                              5   FC-114/MeOH:90/10                                                                        1.61                                                                              1.01                                                                              no       95  89 17  13 ND                              6   FC-114/MeOH:90/10                                                                        1.76                                                                              1.08                                                                              no       93  82 49  31 41                              __________________________________________________________________________     ND = not determined                                                           (1) parts of blowing agent mixed in per hundred parts of polymer              (2) through (11) = the same as in Table B                                     (12) FC12 = dichlorofluoromethane, FC114 = dichlorotetrafluoroethane, EtO     = ethanol, MeOH = methanol                                                    (13) parts of talcum powder mixed in per hundred parts of polymer        

EXAMPLE V

The apparatus used in this example is the same as that used in ExampleI.

The polymer used in this example was a terpolymer of styrene,acrylonitrile and hydroxy ethylacrylate (75% styrene, 25% acrylonitrileand 0.22% HEA) having about 157,000 molecular weight. The polymer wasfed into the extruder at an essentially uniform rate of about 10 poundsper hour. A 70/30 by weight mixture of fluorocarbon 12 (FC-12) andisopropyl alcohol (i-PrOH) was premixed and injected into the extruderat a uniform rate of about 1.6 pounds per hour. For tests incorporatingtitanium isopropoxide, a predetermined amount of the crosslinking agentwas premixed with the blowing agent so that the aimed level could beachieved in the final composition. The extruder zones were maintained atabout 170°, 190° and 200° C. for feeding, melting, metering, and mixingzone, respectively. The temperature of the cooling zone was adjusted sothat the gel would reach a uniform temperature for optimum foamexpansion.

Good quality foams were achieved from the polymer with or without theaddition of titanium isopropoxide. As set forth in Table E, the linepressures went up slightly but the increases were probably due to theslight drop in the foaming gel temperature. The increase of the diepressure within the tolerable range is desirable in the extrusionprocess since the enhanced die pressure permits us to achieve the largerfoam cross-section without incurring prefoaming. A control formulation,i.e., without crosslinking agent, Test 1, resulted in prefoaming at thegiven condition while those containing titanium isopropoxidecrosslinking agent produced good foams free from prefoaming. The foamstrands had oval cross-section of about 0.7-1.0 inches in the smallerdiameter and 1.0-1.4" in the larger diameter. As shown in Table F, thefoams had densities of about 2.4-2.5 pcf and expansion ratios of about24-27. The expansion ratio is defined by the ratio of specific foamvolume to polymer volume.

The distinct benefit of titanium isopropoxide addition was seen duringsecondary expansions of the foam products with hot air or atmosphericsteam. As shown in Table F, titanium isopropoxide makes the foams expandsignificantly better in both air and steam. Its effect is mostpronounced in steam expansion. The foam made with 0.34 pph titaniumisopropoxide expands to a size almost twice as large as the control. Thehighly expanded foam products were light and resilient with their thinflexible cells walls. The details of expansion procedures are describedbelow.

For both expansion tests, foams aged for about a week were employed. Forhot air expansion tests, foam strands were sliced to about 3/4" inlength. The specimens were subjected to hot air in a convective ovenmaintained at a predetermined constant temperature for one hour. Theweight and volume of a foam specimen before and after the expansion testwere determined and the expansion ratios were calculated. Among fivedifferent temperatures tried ranging from 100° to 120° C., 110° C.provided the best expansions for all compositions and thus the resultsare reported in Table E.

For steam expansion tests, foams were sliced to about 1/4" thick slugsand subjected to atmospheric steam for various periods ranging from fiveseconds to two hours. Foam specimens having undergone expansionsexceeding about 60 expansion ratio shriveled when taken out of the steambut substantially recovered in about two days. The expansion ratiosreported in Table F are based on the steady state volume determined infive days. All foams attained the maximum expansions during 7 to 15 min.exposure to steam which are set forth in Table F. The longer exposure tosteam resulted in gradual deterioration of expansion.

All foams were found soluble in methyl ethyl ketone (MEK). Approximately0.2 g of each foam was dissolved in about 25 ml of MEK. The resultindicates that there may develop some build-up of molecular weight but ahigh level of crosslinking does not occur with the polymer at the givenlevel of crosslinking agent. Probably, the titanate plasticizes thepolymer and extends the polymer chain slightly resulting in thefavorable steam expansions.

                                      TABLE E                                     __________________________________________________________________________        BA   TPT  FOAMING                                                                              DIE EXTRUD.                                                                             FOAM  INITIAL                                      LEVEL                                                                              LEVEL                                                                              TEMP.  PRES.                                                                             PRES. DENSITY                                                                             EXPANSION                                TEST                                                                              (pph)                                                                              (pph)                                                                              (C.°)                                                                         (psi)                                                                             (psi) (pcf) RATIO                                    NO. (1)  (2)  (3)    (4) (5)   (6)   (7)                                      __________________________________________________________________________    1   15.6 --   134    490 1600  2.40  27                                       2   16.0 0.2  133    580 1790  2.46  24                                       3   16.0 0.34 132    680 1900  2.40  25                                       __________________________________________________________________________                       EXPANSION IN STEAM                                         EXPANSION IN HOT AIR                                                                             (Expansion Ratio) (9)                                      TEST                                                                              (Expansion Ratio) (8)           max                                                                              max time                               NO. 100° C.                                                                     110° C.                                                                     120° C.                                                                     10 sec                                                                            1 min                                                                             10 min                                                                             45 min                                                                            (10)                                                                             (min) (11)                             __________________________________________________________________________    1   33   38   6.3  49  76   90  35  101                                                                              15                                     2   36   41   6.4  54  75  126  19  150                                                                              7                                      3   39   49   8.2  57  101 109  28  182                                                                              7                                      __________________________________________________________________________     All tests were run at the following conditions:                               Nucleator type and level : 0.1 pph BaSt 0.1 pph talc Die gap : 0.110"?        (1) Parts of a 70/30 mixture of fluorocarbon 12/isopropyl alcohol mixed i     a per hundred parts of polymer                                                (2) Parts of titanium isopropoxide mixed in per hundred parts of polymer      (3) Temperature of foaming gel in degrees centigrade                          (4) Pressure at the die in pounds per square inch                             (5) Pressure at the extruder discharge in pounds per square inch              (6) Density in pounds per cubic foot of foam body aged for about a week       (7) Expansion ratio of foam body determined prior to secondary expansions     which were conducted in about a week                                          (8) Expansion ratio of foam body after exposure to hot air at the             specified temperature for one hour                                            (9) Expansion ratio of foam body after exposure to atmospheric steam for      the specified time and aging for 5 days                                       (10) Maximum expansion ratio of foam body after expansion in steam            (11) Steam exposure time corresponding to the maximum expansion ratio    

EXAMPLE VI

The apparatus used in this example is as in Example I.

A granular linear low density polyethylene (LLDPE) having 1.0 melt index(ASTM D-1238-79 Condition E) and 0.935 g/cc density, was uniformly mixedwith 0.1 pph dibutyl tin dilaurate condensation catalyst (commerciallyavailable under the designation T-12 from M&T Chemicals, Inc.) and 0.1pph talcum powder. The mixture was fed into the extruder at anessentially uniform rate of about 10 pounds per hour. An 80/20 ofFC-12/ethanol blowing agent was injected into the extruder at a rate of19.9 pph. The temperatures maintained at the extruder zones were 170° C.at feeding zone, 220° C. at melting and metering zone, and 220° C. atmixing zone. The temperature of the cooling zone was adjusted so thatthe gel could be cooled down to about 123° C. throughout the tests.

Again, alcohol suppressed line pressures for formulations crosslinkedwith azido functional silane. Good quality foams were obtained at thesilane levels of 0.1 to 0.15 pph. At 0.25 pph silane level, the foamstrand fractured signifying over-crosslinking. The foams made with 0.15and 0.25 pph silane showed some thermo-collapse resistance during ovenaging tests. That is, these foams retained over 50% of their originalvolume during aging in 130° C. oven for one hour while the control andthose containing a lower level of silane collapsed totally during thetest.

                                      TABLE F                                     __________________________________________________________________________             AZIDO                                                                    BA   SILANE                                                                              GEL   DIE DIE   EXTRUDER                                           LEVEL                                                                              LEVEL TEMP. GAP PRESS.                                                                              PRESS.                                         TEST                                                                              (pph)                                                                              (pph) (°C.)                                                                        (in)                                                                              (psig)                                                                              (psig)                                         NO. (1)  (2)   (3)   (4) (5)   (6)                                            __________________________________________________________________________    1   18.0 --    123   0.115                                                                             278   1350                                                                0.105                                                                             290   1390                                                                0.080                                                                             315   1380                                                                0.075                                                                             320   1390                                                                0.070                                                                             369   1405                                           2   18.0 0.05  123   0.090                                                                             322   1440                                                                0.080                                                                             380   1460                                                                0.075                                                                             385   1480                                                                0.070                                                                             360   1570                                           3   18.0  0.075                                                                              123   0.090                                                                             365   1480                                                                0.080                                                                             343   1510                                                                0.075                                                                             350   1320                                           4   18.7 0.10  123   0.090                                                                             400   1520                                                                0.080                                                                             410   1550                                                                0.075                                                                             437   1605                                           5   18.7 0.15  123   0.090                                                                             418   1610                                                                0.080                                                                             460   1660                                                                0.075                                                                             558   1770                                           6   18.0 0.25  123   0.160                                                                             483   1750                                                                0.150                                                                             500   1910                                           __________________________________________________________________________        FOAM FOAM FOAM   CELL                                                                             OPEN                                                      THICK.                                                                             WIDTH                                                                              DENSITY                                                                             SIZE                                                                              CELL                                                                              FOAM  FLOW                                        TEST                                                                              (in) (in) (pcf) (mm)                                                                              (%) APPEAR.                                                                             STAB.                                       NO. (7)  (8)  (9)   (10)                                                                              (11)                                                                              (12)  (13)                                        __________________________________________________________________________    1   0.66 0.96 1.78  0.56                                                                              67  PC    --                                              0.71 1.20 1.77  0.50                                                                              68  B     R                                               0.48 1.01 1.74  0.98                                                                              50  B     R                                               0.52 0.90 1.59  0.46                                                                              28  G     R                                               0.45 0.95 1.70  0.54                                                                              15  E     G                                           2   0.52 0.95 1.52  0.59                                                                              16  B,H   R                                               0.54 1.06 1.33  0.46                                                                              16  G     R                                               0.48 0.97 1.48  0.54                                                                              20  E     R                                               0.54 1.05 1.42  0.33                                                                              11  E     E                                           3   0.60 0.90 1.65  0.45                                                                              19  H     R                                               0.55 1.02 1.59  0.46                                                                              20  E     R                                               0.53 0.98 1.54  0.41                                                                              15  E     E                                           4   0.61 0.91 1.58  0.39                                                                              16  H     R                                               0.55 1.05 1.87  0.40                                                                              20  G     R                                               0.54 1.06 1.48  0.38                                                                               8  E     E                                           5   0.54 1.05 1.60  0.46                                                                              14  G     R                                               0.54 1.03 1.80  0.35                                                                               9  E     R                                               0.56 1.08 1.46  0.42                                                                               7  E     E                                           6   1.02 1.19 1.52  0.41                                                                              16  E     F                                               1.06 1.25 1.57  0.39                                                                              12  E     F                                           __________________________________________________________________________     (1) an 80/20 by weight mixture of FC12 and ethanol mixed in per hundred       parts of polymer                                                              (2) parts of effective azido functional silane mixed in per hundred parts     of polymer; the azidosilane used was CT2905, 50/50 by weight solution of      2(trimethoxysilyl ethylphenylsulfonyl azide) in methylene chloride            marketed by Petrarch Systems, Inc.                                            (3) temperature in degrees centigrade to which the gel was cooled down        prior to foam expansion                                                       (4) gap of die opening in inches at which samples were taken                  (5), (6) pressure in pounds per square inch at the die and at the extrude     discharge, respectively                                                       (7), (8) thickness and width of foam body in inches measured within about     five minutes after extrusion                                                  (9) density of foam body in pounds per cubic foot measured in about one       month                                                                         (10) open cell content in percent determined per ASTM D2856-A                 (11) cell size in millimeter in horizontal direction determined per ASTM      D3576                                                                         (12) subjective judgment of foam appearance; C = total collapse, PC =         partial collapse, O = open cells B = blips or large voids contained in th     foam, V = voids of smaller dimensions contained in the foam, H = hairy        skin originating from prefoaming, G = good, E =  excellent                    (13) the behavior of extrudate; W = wobbly strand, S = surging, R =           ripples at the edges, F = melt fracture, G = good, E = excellent         

EXAMPLE VII

In this example, the same apparatus as in Example I was used. A highdensity polyethylene (HDPE) having 0.6 melt index (ASTM D-1238-79Condition E) and 0.963 g/cc density was used in this example. Thepolymer granules were mixed with 0.05 pph talc and 0.05 pph organotincatalyst (T-12). The mixture was fed into the extruder at 10 pounds perhour. Extruder zones were maintained at 160, 200 and 200° C. forfeeding, melting and metering, and mixing zone, respectively. The geltemperaure was maintained at about 130° C. and a 90/10 mixture ofFC-12/EtOH was used as the blowing agent. The test results are presentedin Table G.

Again, the silane crosslinking agent aided in foam processing andalcohol suppressed development of crosslinking in the extrusion line. Ata low silane level, improvements were seen in one or more performanceareas. For example, even at 0.05 pph silane level, foam density droppedsignificantly from the control. At 0.15 pph silane level, good qualityfoams were produced with a noticeable increase in the die pressure.Interestingly, the pressure at extruder discharge increased little atthis silane level. This is an advantage in foam extrusion process sincewe like to have a high die pressure to prevent prefoaming but a lowextruder discharge pressure to facilitate polymer extrusion. The trendindicates that the alcohol-containing blowing agent called for a silanelevel higher than 0.15 pph for the optimum results.

                                      TABLE G                                     __________________________________________________________________________             AZIDO                                                                    BA   SILANE                                                                              GEL   DIE DIE   EXTRUDER                                           LEVEL                                                                              LEVEL TEMP. GAP PRESS.                                                                              PRESS.                                         TEST                                                                              (pph)                                                                              (pph) (°C)                                                                         (in)                                                                              (psig)                                                                              (psig)                                         NO. (1)  (2)   (3)   (4) (5)   (6)                                            __________________________________________________________________________    1   17.8 --    129   0.105                                                                             265   1200                                                                0.100                                                                             260   1190                                           2   17.8 0.05  130   0.105                                                                             260   1180                                           3   17.8  0.075                                                                              130   0.105                                                                             300   1190                                           4   17.8 0.10  130   0.110                                                                             288   1160                                                                0.105                                                                             280   1160                                                                0.100                                                                             300   1160                                           5   17.8 0.15  130   0.110                                                                             310   1200                                                                0.105                                                                             310   1195                                                                0.100                                                                             380   1250                                           __________________________________________________________________________        FOAM FOAM FOAM  CELL                                                                              OPEN                                                      THICK.                                                                             WIDTH                                                                              DENSITY                                                                             SIZE                                                                              CELL                                                                              FOAM  FLOW                                        TEST                                                                              (in) (in) (pcf) (mm)                                                                              (%) APPEAR.                                                                             STAB.                                       NO. (7)  (8)  (9)   (10)                                                                              (11)                                                                              (12)  (13)                                        __________________________________________________________________________    1   0.76 1.19 2.27  0.45                                                                              84.2                                                                              B     W                                               0.82 1.17 2.19  0.41                                                                              82.9                                                                              V     W                                           2   0.71 1.18 1.75  0.48                                                                              87.4                                                                              V     W                                           3   0.83 1.20 1.80  0.48                                                                              87.7                                                                              V     W                                           4   0.78 1.16 1.81  0.39                                                                              84.7                                                                              V     W                                               0.70 1.07 1.76  0.40                                                                              85.9                                                                              V     G                                               0.78 1.22 1.66  0.70                                                                              61.8                                                                              V     W                                           5   0.96 1.24 1.50  0.74                                                                              57.3                                                                              G     G                                               0.80 1.18 1.49  0.60                                                                              56.5                                                                              G     G                                               0.95 1.21 1.44  0.90                                                                              46.8                                                                              G     G                                           __________________________________________________________________________     (1) parts of 90/10 by weight mixture of FC12/ethanol mixed in per hundred     parts of polymer                                                              (2) parts of effective azido functional silane mixed in per hundred parts     of polymer; the azido silane used was CT2905, a 50/50 by weight solution      of 2(trimethoxysilyl ethylphenylsulfonyl azide) in methylene chloride         marketed by Petrarch Systems, Inc.                                            (3) temperature in degrees centigrade to which the gel was cooled down        prior to foam expansion                                                       (4) gap of die opening in inches at which samples were taken                  (5), (6) pressure in pounds per square inch at the die and at the extrude     discharge, respectively                                                       (7), (8) thickness and width of foam body in inches measured within about     five minutes after extrusion                                                  (9) density of foam body in pounds per cubic foot measured in about one       month                                                                         (10) open cell content in percent determined per ASTM D2856-A                 (11) cell size in millimeter in horizontal direction determined per ASTM      D3576                                                                         (12) subjective judgment of foam appearance; C=total collapse, PC =           partial collapse, O = open cells, B = blips or large voids contained in       the foam, V = voids of smaller dimensions contained in the foam, H = hair     skin originating from prefoaming, G = good, E = excellent                     (13) the behavior of extrudate; W = wobbly strand, S = surging, R =           ripples at the edges, F = melt fracture, G = good, E = excellent         

EXAMPLE VIII

The same apparatus used in Example I was used in this example. Thepolymer feedstock employed in this example was an 80/20 mixture of alinear low density polyethylene (1.0 M.I., 0.935 g/cc density) and apolystyrene having an average molecular weight of about 200,000. Twogranular polymers were blended by use of a tumbler, mixed with 0.1 pphtalc and 0.05 pph organotin catalyst (T-12) and fed to the extruder atan essentially uniform rate of 10 pounds per hour. A 95/5 by weightmixture of FC-12/ethanol was injected into the extruder at a rate ofapproximately 21.0 pph. Extruder zones were maintained at 145°, 195° and205° C., for feeding, melting and metering, and mixing zone,respectively. The gel was cooled down to an essentially uniformtemperature of about 122° C. The test results are shown in Table H.

This particular polymer blend provided reasonably good foam withoutcrosslinking when the die gap was closed down to 0.050 inch. The foamhad a small cross section and a relatively high level of open cells. Ata larger die gap, foam collapsed partially. Foam improved progressivelywith the azido functional silane level. At a silane level of 0.15 pph orhigher, superb-looking foams were obtained having a lower density,larger cross-section, and lower open cell content. At a silane level ashigh as 0.25 pph, there was no sign of over-crosslinking.

The foams thus produced also had excellent dimentional stability duringaging without suffering any shrinkage. The heat distortion temperatureof the blend foams was about 110° C.

                                      TABLE H                                     __________________________________________________________________________             AZIDO                                                                    BA   SILANE                                                                              GEL   DIE DIE   EXTRUDER                                           LEVEL                                                                              LEVEL TEMP. GAP PRESS.                                                                              PRESS.                                         TEST                                                                              (pph)                                                                              (pph) (°C.)                                                                        (in)                                                                              (psig)                                                                              (psig)                                         NO. (1)  (2)   (3)   (4) 92.9  (6)                                            __________________________________________________________________________    1   20.3 --    122   0.070                                                                             328   1020                                                                0.065                                                                             332   1040                                                                0.060                                                                             342   1050                                                    ND          0.055                                                                             348   1070                                                          20.7  0.050                                                                             430   1150                                           2   21.0 0.1   122   0.070                                                                             330   1040                                                                0.065                                                                             330   1050                                                                0.060                                                                             332   1060                                                                0.055                                                                             339   1090                                                                0.050                                                                             420   1250                                           3   21.0 0.15  122   0.080                                                                             365   1150                                                                0.070                                                                             372   1180                                                                0.065                                                                             380   1200                                                                0.060                                                                             390   1240                                                                0.055                                                                             442   1330                                           4   21.0 0.2   122   0.080                                                                             410   1220                                                                0.075                                                                             415   1250                                                                0.070                                                                             425   1300                                           5   21.0 0.25  122   0.080                                                                             440   1325                                                                0.075                                                                             460   1350                                                                0.070                                                                             510   1600                                           __________________________________________________________________________        FOAM FOAM FOAM  CELL                                                                              OPEN                                                      THICK.                                                                             WIDTH                                                                              DENSITY                                                                             SIZE                                                                              CELL                                                                              FOAM  FLOW                                        TEST                                                                              (in) (in) (pcf) (mm)                                                                              (%) APPEAR.                                                                             STAB.                                       NO. (7)  (8)  (9)   (10)                                                                              (11)                                                                              (12)  (13)                                        __________________________________________________________________________    1   0.42 1.06 1.91  0.42                                                                              92.9                                                                              PC    --                                              0.43 1.03 2.14  0.44                                                                              93.2                                                                              PC    --                                              0.42 1.04 1.76  0.43                                                                              95.6                                                                              PC    --                                              ND   ND   ND    ND  ND  B     W,R                                             0.53 1.17 1.39  0.32                                                                              20.7                                                                              E     E                                           2   0.66 1.10 2.00  0.42                                                                              92.9                                                                              PC    --                                              0.43 1.05 1.51  0.39                                                                              87.9                                                                              PC    --                                              0.44 1.03 1.70  0.43                                                                              85.9                                                                              B     W                                               0.43 1.10 2.15  0.40                                                                              83.8                                                                              B     W                                               0.50 1.28 1.44  0.32                                                                              7.20                                                                              E     G                                           3   0.70 1.14 1.45  0.46                                                                              50.1                                                                              B     W                                               0.65 1.24 1.42  0.32                                                                              36.3                                                                              V     W                                               0.60 1.14 1.26  0.35                                                                              22.9                                                                              V     G                                               0.63 1.17 1.32  0.35                                                                              10.1                                                                              E     G                                               0.60 1.25 1.19  0.32                                                                              8.1 E     E                                           4   0.75 1.18 1.24  0.34                                                                              3.7 V     W                                               0.70 1.20 1.41  0.37                                                                              10.0                                                                              E     E                                               0.72 1.25 1.38  0.40                                                                              8.5 E     E                                           5   0.72 1.28 1.26  0.36                                                                              9.2 E     G                                               0.77 1.22 1.42  0.37                                                                              15.4                                                                              E     E                                               0.75 1.28 1.17  0.36                                                                              11.0                                                                              E     E                                           __________________________________________________________________________     WD = not determined                                                           (1) parts of 95/5 by weight mixture of FC12/ethanol mixed in per hundred      parts of polymer                                                              (2) parts of effective azido functional silane mixed in per hundred parts     of polymer; the azido silane used was CT2905, a 50/50 by weight solution      of 2(trimethoxysilyl ethylphenylsulfonyl azide) in methylene chloride         marketed by Petrarch Systems, Inc.                                            (3) temperature in degrees centigrade to which the gel was cooled down        prior to foam expansion                                                       (4) gap of die opening in inches at which samples were taken                  (5), (6) pressure in pounds per square inch at the die and at the extrude     discharge, respectively                                                       (7), (8) thickness and width of foam body in inches measured within about     five minutes after extrusion                                                  (9) density of foam body in pounds per cubic foot measured in about one       month                                                                         (10) open cell content in percent determined per ASTM D2856-A                 (11) cell size in millimeter in horizontal direction determined per ASTM      D3576                                                                         (12) subjective judgment of foam appearance; C = total collapse, PC =         partial collapse, O = open cells, B = blips or large voids contained in       the foam, V = voids of smaller dimensions contained in the foam, H = hair     skin originating from prefoaming, G = good, E = excellent                     (13) the behavior of extrudate; W = wobbly strand, S = surging, R =           ripples at the edges, F = melt fracture, G = good, E = excellent         

EXAMPLE IX

The apparatus in this example is the same as in Example I. The polymerfeedstock employed for tests in this example was a 50/50 by weight blendof polystyrene with Mw 200,000 and polystyrene with Mw 300,000.Approximately 0.05 pph T-12, 0.1 pph barium stearate and 0.1 pph talcumpowder were mixed in the granular blend of two polystyrenes and fed intothe extruder at a uniform rate of 10 pounds per hour. A 70/30 by weightmixture of FC-12 and isopropyl alcohol was used as the blowing agent.The level of azido silane crosslinking agent (2-trimethoxyoilyl ethylphenyl sulfonyl) azide, was varied up to 0.45 pph. The extruder zoneswere maintained at about 170°, 200° and 200° C. for feeding, melting andmetering, and mixing zone, respectively. The temperature of the coolingzone was adjusted so that the gel could reach an essentially uniformtemperature of about 135° C.

When the operating condition reached an essentially steady state, theeffects of die opening on foam appearance and line pressures werestudied. Foam samples were taken both at the threshold die gap forprefoaming and at a fixed die gap for a given blowing agent system.Property determination and secondary foaming tests were conducted. Thefoam samples were aged for about one month.

Secondary foaming was conducted both by atmospheric steam and by hotair. Foam slugs of about 0.25" thickness were sliced out of foam strandsand aged for about one day at ambient temperature prior to secondaryexpansions. After exposure to atmospheric steam for varying lengths oftime, foam specimens were aged at ambient temperature while theirweights and volumes were monitored. Highly expanded foam specimensshrank when taken out of steam but recovered to the final steady statevolume in about two days. Expansion tests in hot air were conductedsimilarly with the exception that expansion or shrinkage of a foamspecimen in the oven was permanent not needing ambient aging for volumerecovery.

The process data set forth in Table I manifest the crosslinking-delayingeffect of alcohol in the foam extrusion line. With this blowing agentalso, we see the general effects of azido silane on foam extrusion andsecondly expansions.

                                      TABLE Ia                                    __________________________________________________________________________                          AZIDO                                                                              FOAMING                                                                              THRESHOLD FOR PREFOAMING                    BLOWING AGENT         SILANE                                                                             GEL    DIE DIE  FOAM FOAM                          TEST                                                                              TYPE    RATIO                                                                              LEVEL                                                                              LEVEL                                                                              TEMP.  GAP PRESS.                                                                             THICK.                                                                             WIDTH                         NO. (1)     (2)  (3)  (4)  (5)    (6) (7)  (8)  (9)                           __________________________________________________________________________    1   FC-12/i-PrOH                                                                          70/30                                                                              15.0 --   134    0.071                                                                             490  0.65 1.11                          2   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.05 134    0.071                                                                             485  0.74 1.10                          3   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.1  134    0.071                                                                             485  0.77 1.27                          4   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.15 134    0.071                                                                             470  0.76 1.12                          5   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.20 134    0.071                                                                             465  0.79 1.17                          6   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.25 135    0.071                                                                             510  0.80 1.17                          7   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.35 135    0.080                                                                             415  0.96 1.32                          8   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.45 135    0.080                                                                             445  0.97 1.43                          __________________________________________________________________________        SAMPLING      EXTRUDER                 FOAM  CELL                         TEST                                                                              DIE GAP                                                                              DIE PRESS.                                                                           PRESS. FOAM THICK.                                                                            FOAM WIDTH                                                                             DENSITY                                                                             SIZE                         NO. (10)   (11)   (12)   (13)     (14)     (15)  (16)                         __________________________________________________________________________    1   0.071  490    910    0.65     1.11     2.12  0.37                         2   0.071  485    950    0.74     1.10     1.87  0.39                         3   0.071  485    950    0.77     1.27     1.90  0.37                         4   0.071  470    950    0.76     1.12     1.85  0.49                         5   0.071  465    930    0.79     1.17     1.76  0.46                         6   0.071  510    1040   0.80     1.33     1.99  0.65                         7   0.071  515    1000   0.89     1.13     1.90  0.74                         8   0.071  565    1050   0.85     1.45     1.95  0.52                         __________________________________________________________________________     (1) FC12 = dichlorodifluoromethane, iPrOH = isopropyl alcohol                 (2) mixture ratio by weight of the component blowing agents                   (3) parts of blowing agent mixed in per hundred parts of polymer              (4) parts of azido functional silane mixed in per hundred parts of polyme     (5) temperature of foaming gel in degrees centigrade                          (6) the gap of die opening in inches at the threshold of prefoaming           (7) pressure at the die in pounds per square inch at the threshold of         prefoaming                                                                    (8) thickness of foam body in inches at the threshold of prefoaming           (9) width of foam body in inches at the threshold of prefoaming               (10) the gap of die opening in inches where the foam sample was taken         (11) pressure at the die in pounds per square inch at the sampling die        opening                                                                       (12) pressure at the extruder discharge in pounds per square inch at the      sampling die opening                                                          (13) thickness of foam body in inches determined after aging for about a      month                                                                         (14) width of foam body in inches determined after aging for about a mont     (15) density of foam body in pounds per cubic foot determined after aging     for about a month                                                             (16) cell size in millimeter in horizontal direction determined per ASTM      D3576                                                                    

                                      TABLE Ib                                    __________________________________________________________________________    BLOWING AGENT            AZIDO SILANE                                                                           INITIAL EXPANSION                           TEST                                                                              TYPE     RATIO LEVEL LEVEL    RATION                                      NO. (1)      (2)   (3)   (4)      (5)                                         __________________________________________________________________________    1   FC-12/i-PrOH                                                                           70/30 15.0  --       30.1                                        2   FC-12/i-PrOH                                                                           70/30 15.0  0.05     30.6                                        3   FC-12/i-PrOH                                                                           70/30 15.0  0.1      29.0                                        4   FC-12/i-PrOH                                                                           70/30 15.0  0.15     31.5                                        5   FC-12/i-PrOH                                                                           70/30 15.0  0.2      32.1                                        6   FC-12/i-PrOH                                                                           70/30 15.1  0.25     29.7                                        7   FC-12/i-PrOH                                                                           70/30 15.1  0.35     31.1                                        8   FC-12/i-PrOH                                                                           70/30 15.1  0.45     31.3                                        __________________________________________________________________________    EXPANSION RATIO AFTER EXPANDING IN STEAM FOR (6)                              TEST                                                                              15 30 1   3  5  7  10 12 15 20 30 45 1  2                                 NO. sec.                                                                             sec.                                                                             min.                                                                              min.                                                                             min.                                                                             min.                                                                             min.                                                                             min.                                                                             min.                                                                             min.                                                                             min.                                                                             min.                                                                             hr.                                                                              hrs.                              __________________________________________________________________________    1   46.5                                                                             81.9                                                                             98.6                                                                              121                                                                              134                                                                              147                                                                              137                                                                              144                                                                              143                                                                              144                                                                              143                                                                              125                                                                              126                                                                              112                               2   51.1                                                                             80.8                                                                             102 129                                                                              137                                                                              146                                                                              155                                                                              153                                                                              160                                                                              154                                                                              156                                                                              153                                                                              147                                                                              131                               3   50.8                                                                             78.8                                                                             102 123                                                                              133                                                                              152                                                                              155                                                                              157                                                                              174                                                                              161                                                                              166                                                                              137                                                                              150                                                                              150                               4   58.2                                                                             91.4                                                                             106 133                                                                              148                                                                              156                                                                              137                                                                              164                                                                              160                                                                              169                                                                              166                                                                              162                                                                              167                                                                              151                               5   51.6                                                                             91.7                                                                             103 138                                                                              150                                                                              185                                                                              220                                                                              171                                                                              172                                                                              194                                                                              163                                                                              158                                                                              175                                                                              148                               6   51.0                                                                             92.0                                                                             121 154                                                                              179                                                                              197                                                                              209                                                                              174                                                                              192                                                                              190                                                                              201                                                                              170                                                                              122                                                                              134                               7   56.0                                                                             96.7                                                                             117 166                                                                              149                                                                              198                                                                              207                                                                              203                                                                              209                                                                              207                                                                              197                                                                              168                                                                              178                                                                              131                               8   61.2                                                                             99.4                                                                             126 174                                                                              195                                                                              202                                                                              198                                                                              191                                                                              198                                                                              202                                                                              185                                                                              135                                                                              158                                                                              131                               __________________________________________________________________________     (1) FC12 = dichlorodifluoromethane, iPrOH = isopropyl alcohol                 (2) mixture ratio by weight of the component blowing agents                   (3) parts of blowing agent mixed in per hundred parts of polymer              (4) parts of azido functional silane mixed in per hundred parts of polyme     (5) specific volume of foam body aged for about a month divided by            specific volume of the polymer determined prior to steam expansion tests      (6) expansion ratio of foam body determined in about two days after           expansion in steam for given period of time                              

                                      TABLE Ic                                    __________________________________________________________________________                          AZIDO                                                                              INITIAL                                            BLOWING AGENT         SILANE                                                                             EXPANSION                                          TEST                                                                              TYPE    RATIO                                                                              LEVEL                                                                              LEVEL                                                                              RATIO                                              NO. (1)     (2)  (3)  (4)  (5)     3   5  10  15 30  45 60  90                __________________________________________________________________________                                       EXPANSION RATIO AFTER EXPANDING IN                                            HOT AIR AT 115° C. FOR (min)                                           (6)                                        1   FC-12/i-PrOH                                                                          70/30                                                                              15.0 --   30.1    34.7                                                                              44.1                                                                             45.8                                                                              53.6                                                                             56.7                                                                              58.8                                                                             64.1                                                                              15.8              2   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.05 32.0    34.7                                                                              34.4                                                                             54.4                                                                              51.6                                                                             59.2                                                                              64.0                                                                             67.8                                                                              26.7              3   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.1  30.9    31.5                                                                              46.4                                                                             52.5                                                                              52.5                                                                             56.9                                                                              62.1                                                                             65.6                                                                              60.1              4   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.15 33.1    33.1                                                                              45.8                                                                             54.3                                                                              52.5                                                                             59.5                                                                              64.8                                                                             67.4                                                                              49.9              5   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.2  34.1    43.8                                                                              58.2                                                                             54.3                                                                              61.1                                                                             62.1                                                                              64.0                                                                             66.5                                                                              66.8              6   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.25 29.6    35.7                                                                              47.9                                                                             47.3                                                                              51.5                                                                             51.2                                                                              52.5                                                                             57.4                                                                              74.2              7   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.35 30.3    30.2                                                                              48.2                                                                             50.5                                                                              50.0                                                                             51.9                                                                              56.4                                                                             59.9                                                                              74.1              8   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.45 31.0    34.0                                                                              39.7                                                                             55.8                                                                              64.5                                                                             65.8                                                                              65.8                                                                             65.0                                                                              81.9                                                 EXPANSION RATIO AFTER EXPANDING IN                                            HOT AIR AT 120° C. FOR (min)                                           (7)                                        1   FC-12/i-PrOH                                                                          70/30                                                                              15.0 --   30.1    31.1                                                                              33.2                                                                             47.7                                                                              47.7                                                                             11.5                                                                               9.6                                                                              8.4                                                                               7.0              2   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.05 32.0    32.5                                                                              40.1                                                                             56.3                                                                              56.7                                                                             23.1                                                                              12.6                                                                              8.4                                                                               8.1              3   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.1  30.9    36.8                                                                              30.6                                                                             51.6                                                                              56.9                                                                             24.8                                                                              17.2                                                                             13.4                                                                              11.4              4   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.15 33.1    33.3                                                                              40.1                                                                             56.9                                                                              58.8                                                                             40.1                                                                              16.2                                                                             14.3                                                                              11.5              5   FC-12/i-PrOH                                                                          70/30                                                                              15.0 0.2  34.1    47.7                                                                              46.8                                                                             59.2                                                                              57.3                                                                             40.1                                                                              16.2                                                                             13.4                                                                              10.5              6   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.25 29.6    33.1                                                                              40.4                                                                             56.9                                                                              61.4                                                                             58.6                                                                              25.4                                                                             18.4                                                                              13.1              7   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.35 30.3    38.8                                                                              44.4                                                                             61.4                                                                              59.3                                                                             73.5                                                                              31.5                                                                             20.3                                                                              13.7              8   FC-12/i-PrOH                                                                          70/30                                                                              15.1 0.45 31.0    35.0                                                                              50.1                                                                             64.8                                                                              66.5                                                                             80.5                                                                              66.8                                                                             31.5                                                                              21.0              __________________________________________________________________________     (1) FC12 = dichlorodifluoromethane, iPrOH = isopropyl alcohol                 (2) mixture ratio by weight of the component blowing agents                   (3) parts of blowing agent mixed in per hundred parts of polymer              (4) parts of azido functional silane mixed in per hundred parts of polyme     (5) specific volume of foam body aged for about a month divided by            specific volume of the polymer determined prior to steam expansion tests      (6) expansion ratio of foam body after expanding in hot air of 115.degree     C. for specified period                                                       (7) expansion ratio of foam body after expanding in hot air of 120.degree     C. for specified period                                                  

While the methods and compositions herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise methods and compositions, and thatchanges may be made in either without departing from the scope of theinvention, which is defined in the appended claims.

What is claimed is:
 1. A process for preparing lightly crosslinkedolefin or styrene polymer foamed articles having a closed-cellstructure, comprising the steps of:(a) providing an olefin or styrenepolymer material, (b) admixing said olefinic or styrenic polymermaterial with (1) a blowing agent, (2) a crosslinking agent selectedfrom the group consisting of silane, azido silane, titanate and aminocompounds which upon reaction with said olefin or styrene polymermaterial reversibly releases alcohol, and (3) additionally admixing asufficient amount of alcohol to control the degree of crosslinking ofsaid olefin or styrene polymer material in the admixture which isthereby formed, and (c) extruding said admixture and activating saidblowing agent in such a manner to expand said olefin or styrene polymermaterial to a cellular structure and at the same time dissipate saidalcohol, whereby foaming and crosslinking of said olefin or styrenepolymer material concurrently takes place.
 2. The process of claim 1wherein said crosslinking agent is an organofunctional alkoxy silaneselected from the group consisting of gamma-glycidoxypropyltrimethoxysilane, gamma-methacryloxypropyltrimethoxy silane, vinyltrimethoxysilane, vinyltriethoxy silane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-β-(N-vinyl benzyl amino) ethylaminopropyltrimethoxy silane,methyltrimethoxy silane, and gamma-aminopropyl trimethoxy silane.
 3. Theprocess of claim 1 wherein said crosslinking agent is an azido silane ofthe formula R R'SiY₂ in which R represents an azido functional radicalattached to silicon through a silicon to carbon bond and composed ofcarbon, hydrogen, sulfur, nitrogen, or oxygen, each Y represents ahydrolyzable organic radical, and R' represents a monovalent hydrocarbonradical or a hydrolyzable organic radical.
 4. The process of claim 3wherein said crosslinking agent is selected from the group consisting of2-(trimethoxysilyl)ethyl phenyl sulfonyl azide and (triethoxy silyl)hexyl sulfonyl azide.
 5. The process of claim 1 wherein saidcrosslinking agent is a titanate having a general formula Ti(OR)₄ whereR is C₁ to C₁₈ alkyl or having a formula (RO)_(m) --Ti(O-X-R² -Y)_(n)wherein R is alkyl, X is carboxyl, R² is alkyl, Y is a reactive doublebond or amino, and m and n are integers which total
 4. 6. Tne process ofclaim 5 wherein said crosslinking agent is selected from the groupconsisting of titanium isopropoxide, and tetramethyl, titanate.
 7. Theprocess of claim 1 wherein said crosslinking agent is selected from thegroup consisting of hexamethoxymethylmelamine and alkylatedglycoluril-formaldehyde resins.
 8. The process of claim 1 wherein saidolefin or styrene polymer material is selected from the group consistingof linear low density polyethylene, high density polyethylene,polypropylene, polystyrene, styrene/acrylic acid copolymers,ethylene/acrylic acid copolymers, styrene/acrylonitrile/hydroxyethylacrylate terpolymers, and mixtures thereof.
 9. The process of claim8 wherein said alcohol is an aliphatic alcohol selected from the groupconsisting of methanol, ethanol, n-propanol, i-propanol, and butanol.10. The process of claim 9 wherein said blowing agent is selected fromthe group consisting of dichlorodifluoromethane,trichloromonofluoromethane, dichlorotetrafluoroethane and mixturesthereof.
 11. The process of claim 1 wherein said olefin styrene polymermaterial is selected from the group consisting of styrene/acrylic acidcopolymer and ethylene/acrylic acid copolymers and said crosslinkingagent is hexamethoxymethylmelamine.
 12. The process of claim 1 whereinsaid olefin or styrene polymer material is selected from the groupconsisting of linear low density polyethylene, high densitypolyethylene, polystyrene and mixtures thereof and said crosslinkingagent is 2-(trimethoxysilyl) ethyl phenyl sulfonyl azide.
 13. Theprocess of claim 1 wherein said olefin or styrene polymer is astyrene/acrylonitrile/hydroxy ethylacrylate terpolymer and saidcrosslinking agent is selected from the group consisting of titaniumisopropoxide, and tetramethyl titanate.